Because the surface of an ultrasonic probe comes into direct contact with the patient, legal regulations exist such that the surface is below a predetermined temperature (for example, 43° C.) in order to avoid injury such as burns to the patient. As Prior Example 1, a method for controlling ultrasonic wave output by providing a temperature sensor within a probe, for example, is proposed, as shown in Patent Documents 1 and 2, below. In addition, as Prior Example 2, a method for controlling the applied voltage of a probe by software and hardware such that surface temperature does not exceed the regulation value by measuring the relation between the applied voltage of the probe and surface temperature beforehand, in place of providing a temperature sensor, for example, is proposed, as shown in Patent Reference 3, below. Patent Reference 1: Japanese Patent Application Publication No. H7-265315 (FIG. 1, Paragraph 0008) Patent Reference 2: Japanese Patent Application Publication No. 2001-321377 (FIG. 1, Paragraph 0026) Patent Reference 3: Japanese Patent Application Publication No. 2000-5165 (FIG. 1, Paragraph 0020)
However, in the foregoing Prior Example 1 which uses temperature sensor, there is a problem in that it becomes more expensive due to the temperature sensor and, in addition, there is a problem in that the probe surface temperature, which is the test subject contact surface temperature, cannot be measured accurately depending on the arrangement position (Issue 1).
In addition, in the foregoing Prior Example 2 wherein surface temperature is controlled by software and hardware, there is a problem in that the surface temperature sometimes exceeds regulation value due to bugs in the software, runaway software, hardware malfunction and the like. Furthermore, in practice, when ultrasonic waves are received consecutively, the surface temperature gradually rises according to the specific heat of the probe window or internal fluid, and even if the regulation value is not exceeded suddenly, there is a problem in that the sensitivity of ultrasound image is poor because ultrasonic wave output is set excessively low in Prior Example 2 (Issue 2).